Local Thermal Nonequilibrium During Melting of a Paraffin Filled in an Open-Cell Copper Foam: A Visualized Study at the Pore-Scale

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Li-Wu Fan ◽  
Hong-Qing Jin
Keyword(s):  
Thermal Imaging ◽  
Metal Foam ◽  
Pore Scale ◽  
Thermal Nonequilibrium ◽  
Rectangular Cell ◽  
Open Cell ◽  
Copper Foam ◽  
Imaging Results ◽  
Local Thermal Nonequilibrium ◽  
Visualized Study

In this technical brief, the application of infrared thermal imaging to investigate melting of a phase-change material (PCM) filled in an open-cell metal foam was proposed. Melting experiments in a rectangular cell were performed with paraffin/copper foam composite samples having a single pore size of 15 ppi. The visualized study at the pore-scale was enabled using an infrared video camera equipped with a macrolens, offering a resolution of 50 μm. The transient thermal imaging results were first validated against the temperature readings by a pre-installed thermocouple. A relative deviation below 4% was observed between the two methods over the entire course of melting. The local thermal nonequilibrium between a copper ligament and its surrounding paraffin was found to become more pronounced as melting proceeds, which could reach up to the order of 10 °C during the late stage of melting. The quantitative observation of the local thermal nonequilibrium effect may facilitate improvement of the existing two-temperature models for numerical simulations on melting of PCM enhanced by embedding metal foams.

Melting of a Phase Change Material Filled in a Metal Foam: A Visualized Study at the Pore-Scale Using Infrared Imaging

2016 ◽  
Author(s):  
Hong-Qing Jin ◽  
Li-Wu Fan
Keyword(s):  
Phase Change ◽  
Phase Change Material ◽  
Thermal Imaging ◽  
Metal Foam ◽  
Temperature Measurements ◽  
Paraffin Wax ◽  
Pore Scale ◽  
Ir Camera ◽  
Copper Foam ◽  
Change Material

The thermal imaging technique was applied in this work to measure the transient temperature fields during melting of a phase change material (PCM) in a metal foam. A paraffin wax was used as the PCM that was filled in an open-celled copper foam. Melting of a paraffin wax in the presence of copper foam was studied in a rectangular cavity that was heated from one lateral side wall, while the top surface was exposed to an infrared (IR) camera. A thermocouple (TC) was also employed to validate the accuracy of temperature measurements by IR thermal imaging. The relative deviation of measured temperature by the TC and IR camera was found to be under 2% in steady state and under 4% during the entire course of melting. The resolution of IR thermal imaging with the aid of a macro lens allowed for temperature measurements at pore-scale of the copper foam. Local thermal imaging was captured through a minor window on the top plate of the container. Three points (Sp1–3) inside a selected individual pore were marked to quantify the temperature variations of melting process within metal foam/PCM at pore-scale. The average temperature differences between Sp1 and Sp2, Sp3 were found to be about 1 °C over the entire course of melting, and the maximum value was up to nearly 10 °C around the melting point. These preliminary results clearly highlighted the effect of metal ligaments on the temperature distributions at pore-scale.

Numerical Study of Heat Conduction of High Porosity Open-Cell Metal Foam/Paraffin Composite at Pore Scale

2016 ◽  
Author(s):  
Yuanpeng Yao ◽  
Huiying Wu ◽  
Zhenyu Liu
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Pore Size ◽  
Metal Foam ◽  
Foam Cell ◽  
High Porosity ◽  
Pore Scale ◽  
Thermal Equilibrium State ◽  
Foam Structure ◽  
Open Cell

In this paper, a numerical model employing 3D foam structure represented by Weaire-Phelan foam cell is developed to study the steady heat conduction of high porosity open-cell metal foam/paraffin composite at the pore-scale level. Two conduction problems are considered in the cubic representative computation unit of the composite material: one with constant temperature difference between opposite sides of the cubic unit (that can be used to determine the effective thermal conductivity (ETC)) and the second with constant heat flux at the interface between metal foam and paraffin (that can be used to determine the interstitial conduction heat transfer coefficient (ICHTC)). The effects of foam pore structure parameters (pore size and porosity) on heat conduction are investigated for the above two problems. Results show that for the first conduction problem, the effect of foam structure on heat conduction (i.e. the ETC) is related to porosity rather than pore size. The essential reason is due to the thermal equilibrium state between metal foam and paraffin indicated by the negligible interstitial heat transfer. While for the second conduction problem with inherent thermal non-equilibrium effect, it shows that both porosity and pore size significantly influence the interstitial heat conduction (i.e. the ICHTC). Furthermore, the present ETC and ICHTC data are compared to the results in the published literature. It shows that our ETC data agree well with the reported experimental results, and are more accurate than the numerical predications based on body-centered-cubic foam cell in literature. And our ICHTC data are in qualitative agreement with the published numerical results, but the present results are based on a more realistic foam structure.

Pore Scale Investigation of Heat Conduction of High Porosity Open-Cell Metal Foam/Paraffin Composite

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Yuanpeng Yao ◽  
Huiying Wu ◽  
Zhenyu Liu
Keyword(s):  
Heat Conduction ◽  
Pore Size ◽  
Metal Foam ◽  
Volume Fraction ◽  
Experimental Studies ◽  
Scale Model ◽  
Small Scale ◽  
High Porosity ◽  
Pore Scale ◽  
Open Cell

In this paper, a numerical model employing an approximately realistic three-dimensional (3D) foam structure represented by Weaire–Phelan foam cell is developed to study the steady-state heat conduction of high porosity open-cell metal foam/paraffin composite at the pore-scale level. The conduction problem is considered in a cubic representative computation unit of the composite material with a constant temperature difference between one opposite sides of the cubic unit (the other outer surfaces of the cubic unit are thermally insulated). The effective thermal conductivities (ETCs) of metal foam/paraffin composites are calculated with the developed pore-scale model considering small-scale details of heat conduction, which avoids using adjustable free parameters that are usually adopted in the previous analytical models. Then, the reason why the foam pore size has no evident effect on ETC as reported in the previous macroscopic experimental studies is explored at pore scale. Finally, the effect of air cavities existing within solid paraffin in foam pore region on conduction capacity of metal foam/paraffin composite is investigated. It is found that our ETC data agree well with the reported experimental results, and thus by direct numerical simulation (DNS), the ETC data of different metal foam/paraffin composites are provided for engineering applications. The essential reason why pore size has no evident effect on ETC is due to the negligible interstitial heat transfer between metal foam and paraffin under the present thermal boundary conditions usually used to determine the ETC. It also shows that overlarge volume fraction of air cavity significantly weakens the conduction capacity of paraffin, which however can be overcome by the adoption of high conductive metal foam due to enhancement of conduction.

scholarly journals Numerical study of pore-scale flow and noise of an open cell metal foam

2018 ◽  
Vol 82-83 ◽  
pp. 185-198 ◽  
Author(s):  
Chen Xu ◽  
Yijun Mao ◽  
Zhiwei Hu
Keyword(s):  
Metal Foam ◽  
Numerical Study ◽  
Pore Scale ◽  
Open Cell
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